According to Wikipedia, Martin Rapaport started as a cleaver and rough sorter in Antwerp, Belgium. In 1975 he began brokering rough and polished diamonds in New York City and, In 1978, created the Rapaport Prices List.
Since creating the price list, he’s also known for founding many businesses in the diamond industry, including an electronic trading network for traders RapNet and INDEX, and diamond-related news in print and web formats.
The Rapaport Diamond Report price list (“Rap List”) is released weekly on Fridays, however it does not necessarily change every week.
It is used as a baseline for pricing for basically all loose diamonds sold as single individual stones (as opposed to diamonds sold in parcels) generally SI3 or better in clarity and K or better in color (although the price list does offer prices for L and lower colors and I1 and lower clarities, they are rarely used in the industry).